Tube with head made of multilayer materials and manufacturing process

ABSTRACT

A method for manufacturing a tube head including the steps of using a co-injection head having an annular outlet and which can be supplied simultaneously with a thermoplastic structure material A and a thermoplastic barrier material B is disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 09/807,411 filed Oct. 9,2001, the contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the domain of plastic tubes, and particularlytubes with barrier properties, typically for toothpaste tubes.

STATE OF THE ART

European patent EP-B-0524 897 submitted in the name of the applicantdiscloses a process for the manufacture of tubes in which firstly,particularly in order to improve the barrier effect of tube heads, aseparate single part or insert made of a 5-layer multilayer materialPE/adh/EVOH/adh/PE is prepared by thermoforming, where “PE” denotes apolyethylene layer, “EVOH” denotes a vinyl ethylene alcohol copolymerlayer with a barrier effect, “Adh” denotes an adhesive layer to assurecohesion between the PE and EVOH layers,

A tube skirt and the said insert are then placed on a punch of an insertmolding tool, the two being manufactured separately, and the PE head isthen insert molded to obtain a tube as shown in FIG. 1.

Documents AU-0545 604 and EP-A-0130 239 describe other processes formanufacturing tubes including the use of inserts, typicallypolybutyleneterephthalate (PBT) inserts made separately by molding.

Finally, document BE-A-666 719 describes a tube in which the headcomprises an insert in the form of a truncated cone made of a foldedthin sheet of aluminum, as barrier material.

STATEMENT OF THE PROBLEMS

Problems can arise with known tubes according to standard practice, as aresult of using inserts made separately:

firstly, separate manufacturing of an insert, particularly in the caseof an insert with five layers as described in document EP EP-B-0524 897,is an additional operation, for which the manufacturing cost isadditional to the cost of an identical tube without an insert, plus theassembly cost of the insert itself and the increased complexity ofassembly machines,

secondly, the inserts form barrier materials and therefore with adifferent nature from the PE. Since they are made separately, they add anon-negligible percentage to the weight of the tube, and insertmaterials (particularly PBT) are immiscible with PE which is the typicalmaterial used in tubes, introducing a problem with recycling thematerials used in the tubes,

finally, the inserts often create a barrier problem, either because theintrinsic barrier properties of the barrier material are inadequate, orbecause there is an excessive annular band at the connection zonebetween the skirt and the head.

The heads and tubes according to the invention solve all these problemssimultaneously.

DESCRIPTION OF THE INVENTION

According to a first purpose of the invention, the plastic tube head,designed to be assembled with a skirt to form a tube, comprising atypically threaded orifice and a shoulder comprising an annularconnection part to the said skirt, is characterized in that:

-   a) the said head is formed by co-injection and comprises a    multilayer material containing an internal layer, an external layer    in structure material, typically a polyolefine, and at least one    inner layer made of a thermoplastic barrier material,-   b) the said inner layer is encased by the said internal and external    layers, including at the ends of the said head where the said    internal and external layers are joined together in a polyolefine    layer, the distances “e” and “e′” between each of the ends of the    said inner layer and the corresponding end of the said head being    between 0.02 mm and 5 mm and preferably less than 3 mm, such that    the said inner layer made of a barrier material extends over the    greatest possible height, while its ends remain encased or    encapsulated by the junction of the said internal and external    layers.

The invention introduces a radical change in the design of the saidhead, firstly in the sense that the said internal layer is completelyimmersed and encased by a so-called structure material A, typically apolyolefine material—but it may also be another extrudable material suchs a PET or a PA—without discontinuity or break in the material flow asis the case with the use of an insert according to the prior art, andsecondly in that the said inner layer may be extended as far as requiredand as close as required to the ends of the said head, the only limitbeing that this layer is not in contact with the outside and remainsencased by the structure material A.

Since there are no inserts or add-on parts, the tube according to theinvention has several important advantages for persons skilled in theart, concerning the cost, the compatibility of the head and skirtmaterials and therefore recycling, since a typical insert is made ofPBT, a unique material that does not exist in the skirt, and the factthat the performance of the head can be adapted depending on needs,knowing that not all packaged products have the same requirementsconcerning impermeability of the head, and therefore that the nature ofthe barrier layer and its thickness can be varied to obtain tubesadapted to needs at minimum cost.

Said barrier layer may be formed from one or more layers which overlapat least in part.

DESCRIPTION OF THE FIGURES

FIGS. 1 a and 1 b are axial sectional views of a tube head 2 accordingto the state of the art provided with an insert 4. This head has anorifice 20 in which a thread 201 is formed, and a connection shoulder 21to a skirt 3.

FIG. 1 a shows a view of a head 2 with its injection gate 26 at the exitfrom the insert molding station where the head 2 is molded on the skirt3.

FIG. 1 b corresponds to the head of the tube 2 in FIG. 1 a after theinjection gate 26 has been eliminated and after the orifice 200 has beenformed.

FIG. 1 b shows an enlarged view of the section through the skirt 3 thattypically comprises a layer 30 made of a barrier material B coated withan external layer 31 and an internal layer 32 in structure material A.

FIGS. 2 a and 2 b correspond to FIGS. 1 a and 1 b and to the invention.The material forming the head 2 comprises an inner layer made of barriermaterial B 25 coated on the outside with an outer layer 23 and on theinside with an internal layer 24 in structure material A.

FIG. 2 b shows distances denoted “e” and “e′” between the ends of thesaid internal layer 24 and the ends of the head.

FIG. 3 shows a vertical sectional view of a co-injection nozzle 5 with avertical axis of symmetry 10 having a central duct 50, an outer ringduct 52 for injection of material A, a median ring duct 51 for injectionof barrier material B and a common exit opening 53.

FIG. 4 contains a vertical section showing a diagrammatic view of anindividual co-injection device. This device comprises a nozzle 5supplied firstly by material A (typically PE) via an injection devicefor material A comprising upstream a supply channel 633 fitted with avalve or closing slide 635, a proportioning piston 632 supplied withmaterial A from an extruder 63 and fitted with a non-return valve 631,and secondly with barrier material B by a barrier material B distributorcomprising a supply channel 643 fitted with a valve or closing slide 644and, upstream, an extruder 64 of barrier material B.

The nozzle 5 comprises a shutter 65 for its common opening 53 andterminates in an external opening 66 cooperating with the head moldtooling 2 by injection. The nozzle could comprise axial shutter means(not shown) typically slide means, with which to shutter the exit ofmaterial A, that of material B or both materials A and B at the sametime.

The mold tooling typically comprises a die 61 and a punch 60 on which atube skirt 3 has been placed, the space between the die and punchforming cavity 67 in which said head 2 is formed by coinjection. Thepiston 62 applies the punch plus die assembly in contact with the saidexternal opening 66 at a sufficient pressure to inject the said head 2.

In this figure the distributors of material A and material B for thesimultaneous production of several tube heads are not shown.

FIGS. 5 and 6 show another modality of the process and device accordingto the invention.

FIG. 5 is a principle diagram showing in axial section a co-injectiondevice for structure material A (on the left side of the figure) and formaterial B (on the right side of the figure). This figure shows thedistributors of material A 630 and of material B 640, intended to feedsix cavities 67 simultaneously. The supply circuit for material Acomprises an injection piston 632 and a non-return valve 631 used tosupply the co-injection head 6 with material A at the required flow rateand pressure.

The device comprises a closing slide 65 with a slide 650 having 4positions through side movement of the slide 650 which is suppliedeither with multilayer material A and B via opening 53 of nozzle 5, orwith material A only via the side duct 634 for material A which leadseither to cavity 67 or to a drain 68. Slide 650 is shown incross-section in FIGS. 5 and 5 b and in longitudinal section in FIG. 5 ain which the 4 positions are shown:

Position 1: the slide is full, so that none of inlets 53, 634 and noneof the outlets towards the cavity 67 or the drain 68 communicate.

Position 2: the arrival of material A, 634, is made to communicate withcavity 67, the arrival of multilayer material A and B via opening 53being shuttered,

Position 3: the arrival of multiplayer material A and B via opening 53of nozzle 5 is made to communicate with cavity 67, the arrival ofmaterial A, 634, being shuttered.

Position 4: the arrival of multiplayer material A and B via opening 53of nozzle 5 is made to communicate with the drain 68, a position whichis typically used not during the production cycle, but in the event ofstoppage of the said device before re-start up of the production cycle.

FIG. 6 is a perspective view of the distributors of material A, 630, andmaterial B, 640, respectively supplied by the extruders of material A,63, and of material B, 64, which feed the 6 co-injection heads 6 eachcomprising a nozzle 5 and a side duct 634 forming the two inlets to theslide valve 65. This figure does not show the 6 injection pistons formaterial A, 632. This figure shows the arrangement of the slide valves65 each having two “inlets” or feed points 53 and 634, and two “outlets”66 towards cavity 67 and drain 68, these “inlets” and “outlets” forminga cross in a plane perpendicular to the axis of the valve 65.

FIG. 7 is a diagrammatic overhead view of a tube manufacturing unit withsix injection nozzles 5.

FIG. 7 a diagrammatically shows a sectional view of a skirt 3, and FIG.7 b shows a co-injection output tube with a head corresponding to FIG. 2a.

FIG. 8 illustrates the execution of an injection cycle with a totalduration of To+T′, wherein a mold is placed near the co-injection headin the time between 0 and τ and the co-injection of the material iscarried out from the time τ to To, injection of structure material A(typically a polyolefine of PE type) through valve 635 varying from timeT=0 to T=To, whereas the injection of barrier materials B through thevalve or slide 645 starts at time T=t and terminates at time T=To−t′,the duration T′ being a stabilization time.

The axis denoted “P650” shows the position of slide 650 when the deviceused comprises this type of 4-position slide, designated 1 to 4, asshown in FIGS. 5 a and 5 b.

DETAILED DESCRIPTION OF THE INVENTION

The said internal layer 24 and external layer 23 in head 2 of tube (1according to the invention may be made of the same polyolefine,preferably chosen to be a polyethylene or PE, and the said barriermaterial may be chosen from known extrudable barrier materials and ispreferably chosen to be a polyvinyl alcohol or EVOH, but as alreadyindicated the invention is not limited to specific materials, other thanthat these materials must be extrudable or co-extrudable.

Moreover, it is also possible according to the invention to have asstructure material a material A for the external layer 23 and a materialA′ different to the previous one for the internal layer 24.

Preferably, the said multilayer material has a 3-layer “A/B/A”structure, where A and B respectively denote a structure material layer,typically a polyolefine and preferably PE—that is the internal layer 24and external layer 23, and a barrier material layer—that is the innerlayer (25) typically made of EVOH, the layer of barrier material Bhaving an average thickness of between 0.02 and 0.5 mm, and preferablyan average thickness of 0.04 and 0.2 mm, for a total thickness of thesaid 3-layer structure typically equal to 1.2 mm.

It was observed that it is not necessary, according to the invention, toinsert an adhesive layer between the structure material layer A and thebarrier material B, even though materials A and B may not adhere to oneanother, as is the case with PE and EVOH.

Also, layer B may optionally be replaced by several B layers of narrowerthickness, which overlap in full or in part, possibly with layers Ainserted in between.

As already described, the thickness of the barrier material layer may bevaried as a function of the required performances, considering thenature of the packaged product.

Another purpose of the invention consists of the tubes 1 that comprise ahead 2 according to the invention.

Preferably, the assembly of the said skirt and the said head is formedby co-injection of the said head on the said previously formed skirt.

Although the heads can be made separately and then assembled with theskirts, it is advantageous to proceed as shown in FIG. 4, in other wordsforming the head by injection on a skirt, combining the formation of thehead and the head and skirt assembly in a single step, the skirtpossibly being manufactured apart.

Another purpose of the invention consists of a process for manufacturinga multilayer head according to the invention.

In this process:

a) into a cavity 67, formed by the cooperation of a die 61 and a punch60 and using a co-injection head 6 supplied with structure material Aand barrier material B, a flow of structure material A is co-injectedfor a time T=To with, from a time T=t until a time T=To−t′, a flow ofbarrier material corresponding to said inner layer 25, times t and t′being chosen as short as possible such that, after the injection gate 26has been eliminated, the ends 250, 251 of the said inner barriermaterial layer 25 of the said head 2 are entirely encapsulated by thesaid structure material A of the said internal and external layers 24,23, the said ends 250, 251 being separated from the external medium by athickness of at least 20 μm of the said structure material A,

b) injection of the said structure material A is continued for anadditional time T′ equal to at least To, in order to stabilize thequantity of injected structure material.

Typically:

-   -   T₀ can vary from 0.1 s to 1 s    -   To+T′ can vary from 1 s to 3 s    -   t can range from 0.01 To to 0.5 To    -   t′ can range from 0.01 To to 0.65 To

This process will be better understood with reference to FIGS. 3, 4, 5,5 a, 5 b and 8.

It can be clearly seen in FIG. 8 that the injection of the barriermaterial B begins after the injection of structure material A andterminates before the injection of structure material A.

Thus, it is clear that with all means defined by the invention, it ispossible during a full head production cycle T, to regulate theintroduction of each injected material and thus to control bothdistances “e” and “e′”.

Furthermore, these means can also modify the thickness of the barriermaterial layer B at will, by varying the relative flows of the barriermaterial B and structure material A in the co-injection nozzle 5.

A further purpose of the invention is a process for manufacturing tubeshaving a head 2 according to the invention.

According to a first embodiment, a head according to the invention canbe assembled to the skirt by any known means, typically by any type ofweld. But preferably, said head and said skirt are assembled byco-injecting the said head on the said skirt as shown in FIG. 4.

A manufacturing unit using the process according to the invention isshown diagrammatically in FIG. 7. In this industrial process a turntableor carousel 76 with a vertical axis of rotation 77 divided into psectors 71, 72, 73, 74 where p is typically equal to 8 and is indexed inrotation with an angular pitch equal to 360°/p, brings; each sectorsuccessively in front of at least three fixed stations staggered at anangle relative to said axis of rotation, that is a first skirt loadingstation 71 on the said sector of the turntable, then a second station 72for co-injection and insert molding of the said heads on the saidskirts, and a third section at which the tubes 74 are unloaded from thesaid turntable, the residence time of a sector facing each of the fixedstations being equal to the sum To+T′, preferably varying from 1 secondto 3 seconds, and the time interval between two fixed stations beingdetermined particularly by the angular offset between these two fixedstations.

FIG. 7 shows the case in which, with p equal to 8, the angular offsetbetween the co-injection station 72 and the unloading station 74 isequal to a, typically equal to 180°, such that the tube cooling timebetween the co-injection station and the unloading station isapproximately equal to (To+T′).(p/360°).α.

Example Embodiment

All figures (except FIGS. 1 a and 1 b) are related to the invention andillustrate the invention.

The tube heads obtained according to the examples are shown in FIGS. 2 aand 2 b.

The dimensions of these heads are standard dimensions of toothpaste tubeheads, the height of the head being 20 mm and the tube diameter being 35mm.

The materials used are PE for the structure material, and EVOH for thebarrier material.

The thickness of the multilayer material at the shoulder 21 is typically1.2 mm, and the thicknesses of the PE layers 23, 24 and the barriermaterial layer 25 are 1 mm for the outer layer of PE 23, 0.05 mm for theinner layer of EVOH 25 and 0.15 mm for the internal PE layer 24.

The distances “e” and “e′” obtained for the heads are equal to 2 mm.

These heads are made using co-injection nozzles 5 as shown on FIG. 5.

This type of nozzle 5 is supplied with PE via duct 633 and with EVOH viaduct 634, and comprises means for regulating and opening/closing saidducts. Since the quantity of PE is much greater than the quantity ofEVOH, each nozzle 5 comprises a proportioning piston 633 that injects aprecise quantity of PE into the said cavity—a non-return valve 631preventing any backflow of PE. This proportioning piston 633 is filledduring idle time while the tube is being changed.

Nozzle 5 has an orifice 53 which is automatically closed by a non-returnvalve 65 when the cavity 67, formed by cooperation of punch 60 with die61, is not—by means of piston 62—applied against the external orifice 66for the purpose of co-injecting PE and EVOH.

According to one variant of the invention shown in FIGS. 5 to 6, nozzle5 is only used for co-injecting materials A and B, the injection ofmaterial A alone being made via a specific duct 634 which does not crossthrough the nozzle 5, the changeover from one injection type to anotherbeing made by means of a slide valve 65 with a slide 650 which movessideways and has 4 positions as explained in relation to FIGS. 5, 5 a, 5b and 6.

The sequence of a production cycle for a head 2 is illustrated in FIG.8.

The duration of a cycle To+T′ varies from 1 s to 3 s, and is typicallyclose to 2 s.

In order to guarantee good productivity, the co-injection station on theproduction line used to implement the process according to the inventioncomprises six nozzles 5 in parallel, supplied with material A via ductsor supply channels 633, and with material B via channels 643. Theco-injection head 6 in FIG. 6, in addition to direct supply from nozzle5 of material A via channel 633, also comprises a supply of material Avia side channels 643.

In this latter case, in which the co-injection device comprises aparallel supply of material, and in which a slide valve 65 is used witha 4-position slide 650, the line “P650” in FIG. 8 shows the operationduring two production cycles, each one lasting a time To+T′.

Time To comprises the cycle change, the slide being in position “1”, Iwhich there is no flow of material, this cycle change corresponding tothe replacement of the full cavities by empty cavities, and is conductedduring a time interval that is typically less than 0.1 To.

The industrial production line is shown diagrammatically by the overheadview in FIG. 7. It comprises a carousel 76 or turntable rotating aroundits vertical axis 77 divided into 8 sectors that pass in sequence infront of a first station 71 supplying skirts 3, then in front of asecond co-injection station 72 offset at an angle of 90° (360°.2/8) fromthe first, then in front of a third unloading station 74 at an angle of270° from the first station, such that the tube head cooling time on thecarrousel is equal to approximately 4.(T+T′).

The productivity of this line is about 10 000 tubes per hour,substantially equal to 6×3600/(To+T′), where To+T′ is close to 2 s.

ADVANTAGES OF THE INVENTION

The invention provides an advantageous alternative to the state of theart. As already mentioned, the invention is a means of avoiding the useof inserts, which are made separately from a special material and whichact as a barrier material.

Therefore, the invention can solve all problems related to the presenceof inserts, whether in respect of the compatibility of materials andrecycling of tubes, the extension of the insert and its barrier effectover the entire height of the head, the adaptation of the barrier inrelation to the content and conditions of use, or finally in respect ofthe cost of the tubes.

The invention is a means of obtaining EVOH layers as thin as possibleand as desired in relation to required barrier impermeability, whereasan insert needs to have minimum stiffness and therefore a minimumthickness owing to handling requirements and since it must bemanufactured separately.

Therefore, the invention provides a very general means to enable a tubemanufacturer to meet most requirements, particularly regulatory andlegislative requirements, related to tube materials .and theirrecycling.

LIST OF REFERENCES

-   TUBE . . . 1    -   AXIS SYMMETRY OF THE TUBE . . . 10-   TUBE HEAD . . . 2    -   ORIFICE . . . 20        -   OPENING . . . 200        -   THREAD . . . 201        -   UPPER RIM . . . 202    -   SHOULDER . . . 21    -   SKIRT CONNECTION ZONE . . . 22    -   EXTERNAL LAYER . . . 23    -   INTERNAL LAYER . . . 24    -   INNER LAYER (BARRIER-B) . . . 25        -   TOP END OF B . . . 250        -   BOTTOM END OF B . . . 251    -   INJECTION GATE . . . 26-   SKIRT . . . 3    -   BARRIER MATERIAL . . . 30    -   EXTERNAL LAYER . . . 31    -   INTERNAL LAYER . . . 32-   INSERT OF PRIOR ART . . . 4-   CO-INJECTION NOZZLE . . . 5    -   CENTRAL CHANNEL (material A) . . . 50    -   MEDIAN RING DUCT (B) . . . 51    -   OUTER RING DUCT (A) . . . 52    -   COMMON OPENING/DUCT . . . 53-   COINJECTION HEAD . . . 6    -   PUNCH . . . 60    -   DIE . . . 61    -   SMALL PISTON . . . 62    -   EXTRUDER for material A . . . 63        -   DISTRIBUTOR of material A . . . 630        -   NON-RETURN VALVE . . . 631        -   INJECTION PISTON . . . 632        -   SUPPLY CHANNEL (A) . . . 633        -   SIDE CHANNEL (A) . . . 634        -   VALVE (A) . . . 635    -   EXTRUDER for material B . . . 64        -   DISTRIBUTOR of material B . . . 640        -   SUPPLY CHANNEL (B) . . . 643        -   VALVE (B) . . . 644    -   SLIDE VALVE—4-positions . . . 65        -   MOBILE SLIDE . . . 650    -   RING OPENING . . . 66    -   CAVITY between head of punch and die . . . 67    -   DRAIN . . . 68-   TUBE MANUFACTURING UNIT . . . 7    -   SKIRT SUPPLY . . . 70    -   SUPPLY STATION . . . 71    -   COINJECTION STATION . . . 72    -   COOLING STATION . . . 73    -   UNLOADING STATION . . . 74    -   TUBE TRANSFER . . . 75    -   TABLE OR CARROUSEL . . . 76    -   VERTICAL AXIS OF TABLE . . . 77

1. Plastic tube head (2), designed to be assembled with a skirt (3) toform a tube (1), comprising a typically threaded orifice (20) and ashoulder (21) comprising an annular connection part (22) to the saidskirt, characterized in that, a) the said head (2) is formed byco-injection and comprises a thermoplastic multilayer materialcomprising an internal layer (24) and an external layer (23) instructure material A, and at least one inner layer (25) in barriermaterial B, b) the said inner layer (25) is encased by the said internallayer (24) and external layer (23), including at the ends of the saidhead where the said internal and external layers are joined together inone layer, the distances “e” and “e′” between each of the ends (250,251) of the said inner layer and the corresponding end of the said headbeing between 0.02 mm and 5 mm, such that the said inner layer made of abarrier material (25) extends over the greatest possible height, whileits ends remain encased or encapsulated by the junction of the saidinternal layer (24) and external layer (23). 2-16. (canceled) 17.Process for manufacturing a tube head comprising followings steps: a)using a co-injection head which has an annular outlet and which can besupplied simultaneously with a thermoplastic structure material A and athermoplastic barrier material B, b) in the time elapsing from 0 to τ,placing a mold having an annular cavity near the co-injection head suchas said annular outlet is in communication with said cavity; c)co-injecting said materials in said cavity during a time elapsing from τto T0, by carrying out said following steps: c1) injecting the structurematerial A from T to (τ+t), c2) co-injecting structure material A andbarrier material B between (τ+t) and (T0−t′) c3) injecting the structurematerial A from (T0−t′) to T0, until the cavity is filled; d)maintaining the injection pressure on the structure material A for anadditional time T′, which is equal to at least T0, in order to stabilizethe quantity of injected structure material; e) opening the mold thusfilled and extracting the molded piece that comprises an inner layer ofsaid barrier material B, the ends of the said inner barrier beingentirely encapsulated by said structure material A; f) eliminating theinjection gate.
 18. A process according to claim 17, wherein the annularcavity of the mold is formed by the cooperation of a die and a punch.19. A process according to claim 17, wherein the cavity of the mold hasthe shape of the tube head to be manufactured.
 20. A process accordingto claim 19, wherein elapsed times t and t′ are chosen such that theends of the inner layer of material B are separated from the externalmedium by the structure material A, which has a thickness of at least 20μm.
 21. A process according to claim 17, wherein: T0 is between 0.1 sand 1 s T0+T′ is between 1 s and 3 s t is between 0.01 T0 and 0.1 T0 t′is between 0.02 T0 and 0.2 T0
 22. A process for manufacturing acollapsible tube comprising a tube head and a collapsible skirt, whereinsaid head is manufactured by the process of claim 1 and welded on oneend of said skirt.
 23. A process according to claim 22, wherein formingthe said tube head and welding it on the end of the skirt aresimultaneous.
 24. A process according to claim 23, wherein a pluralityof n tube heads are manufactured simultaneously, n being typicallybetween 2 and 16, by using n injection heads supplied with structurematerial A by means of an extruder for material A and a distributor withn arms, and supplied with barrier material B by means of an extruder formaterial B and a distributor with n arms.
 25. A process according toclaim 24, wherein a turntable having a vertical axis of rotation,divided into p sectors, p being typically equal to 8, and indexed inrotation with an angular pitch equal to 360°/p, is rotated tosuccessively bring each sector in front of at least three fixedstations, at different angular positions with respect to the said axisof rotation, that is a first skirt loading station on the said turntablesector, then a second station for co-injection molding of the said headsand simultaneous welding of said heads on the end of the skirts, and athird section at which the tubes are unloaded from the said turntable,the residence time of a sector facing each of the fixed stations beingequal to the sum To+T′, preferably varying from 1 second to 3 seconds,and the time interval between two fixed stations being determinedparticularly by the angular offset between these two fixed stations. 26.Process according to claim 25, wherein the angular offset α between theco-injection station and the unloading station, typically equal to 180°,is such that the tube cooling time between the co-injection station andthe unloading station is approximately equal to (To+T′).(p/360°).α. 27.A device for the manufacturing of tube heads or tubes, using theco-injection process according to claim 19, comprising 1 to nco-injection heads according to the number n of tube heads to bemanufactured simultaneously in 1 to n corresponding cavities, whereineach of said co-injection heads comprises: a) a co-injection nozzle,which is supplied with structure material A and barrier material B; b)an annular outlet leading to the cavity of the mold, which may besupplied alternatively with material A via an external channel and withan annular flux of material A/B/A via the opening of said co-injectionnozzle supplied with materials A and B, and c) means for ensuring theprogrammed injection of material A or of said annular flux A/B/A/ intosaid cavity at predetermined times in the production cycle.
 28. Deviceaccording to claim 27, wherein said means for ensuring said programmedinjection is a slide valve.
 29. Device according to claim 28, whereinsaid slide valve has 4 positions: I. closing of opening of saidco-injection nozzle and said external channel: in said position, nomaterial flows; II. placing said external channel in communication withthe cavity of the mold: in said position, material A is injected intosaid cavity; III. placing said opening of said co-injection nozzle incommunication with said cavity: in said position, said annular flux ofmultilayer material A/B/A/ is injected into said cavity; IV. placing theopening of said co-injection nozzle in communication with the outsidefor an optional draining of said opening.